Identifying suitable processing window is necessary but difficult for achieving favorable microstructure and performance in extrusion of large thick-walled pipe with difficult-to-deform Inconel 625 alloy. In this work...Identifying suitable processing window is necessary but difficult for achieving favorable microstructure and performance in extrusion of large thick-walled pipe with difficult-to-deform Inconel 625 alloy. In this work, a method was established for identifying the extrusion process window considering temperature control using response surface methodology. Firstly, the response surface models, which correlate temperature rise and peak temperature to key extrusion parameters, have been developed by orthogonal regression based on finite element calculated data. Secondly, the coupled effects of the key extrusion parameters on the temperature rise and peak temperature have been disclosed based on the regression models. Lastly, suitable extrusion processing windows, which are described by contour map of peak temperature in the space of extrusion speed and initial billet temperature, have been established for different extrusion ratios. Using the identified process window, a suitable combination of the key extrusion parameters can be determined conveniently and quickly.展开更多
The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testin...The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testing was performed in various Zn and Mg contents under different annealing and cold-rolling conditions. In the results, the stress drop and reloading time of serrations increase with increasing plastic strain and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg or Zn content. The alloys with a greater intensity of serrated yielding generally exhibit a greater elongation. The stress drop and reloading time of serrations decrease with increasing grain size in the case of the annealed samples. The cold-rolled sample exhibits the most severe serra- tion because it initially contains a large number of grain boundaries and dislocations.展开更多
Austempered ductile iron(ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called...Austempered ductile iron(ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called "ausferrite" that is the result of austempering heat treatment applied to ductile irons. Alloying elements increase ADI austemperability and change speeds of austempering reactions. Thus, they can affect ADI resultant microstructure and mechanical properties. In this paper, the effects of alloying elements on ADI mechanical properties, microstructural changes, two-stage austempering reactions, processing windows, austemperability, and other aspects are reviewed.展开更多
This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing(DIP) and discrete element method(DEM). The results showed that the X-ray diffraction(...This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing(DIP) and discrete element method(DEM). The results showed that the X-ray diffraction(XRD)-based DIP method effectively analyzed the mineral composition contents and spatial distributions of granite. During the particle flow code(PFC2D) model calibration phase, the numerical simulation exhibited that the uniaxial compressive strength(UCS) value, elastic modulus(E), and failure pattern of the granite specimen in the UCS test were comparable to the experiment. By establishing 351 sets of numerical models and exploring the impacts of mineral composition on the mechanical properties of granite, it indicated that there was no negative correlation between quartz and feldspar for UCS, tensile strength(σ_(t)), and E. In contrast, mica had a significant negative correlation for UCS, σ_(t), and E. The presence of quartz increased the brittleness of granite, whereas the presence of mica and feldspar increased its ductility in UCS and direct tensile strength(DTS) tests. Varying contents of major mineral compositions in granite showed minor influence on the number of cracks in both UCS and DTS tests.展开更多
In this work, completely immiscible polyethylene/polyamidel2 （PE/PA12） blends were prepared by high shear extruder. The morphology and mechanical properties of the blends were investigated as a function of rotation ...In this work, completely immiscible polyethylene/polyamidel2 （PE/PA12） blends were prepared by high shear extruder. The morphology and mechanical properties of the blends were investigated as a function of rotation speed. It was found that the high shear processing is an effective method to improve the dispersion of the PAl2 phase in PE matrix when PA 12 contents are 5 wt% and 10 wt%, and the dispersed phase particle size is reduced with the increase of rotation speed from 100 r/min to 500 r/min. However, with further increase of PAl2 content to 20 wt%, high shear processing has no effect on the phase morphology of the blends. Accordingly, a largely increased elongation at break and impact strength are observed for PE/PAl2/95/5 and PE/PA12/90/10 blends obtained at high rotation speeds but no effect on the property of PE/PAI2/80/20. Annealing experiment demonstrated that the obtained phase morphology is not stable thus compatibilizer should be introduced in the future work. This work could provide a guideline for the application of high shear processing in the preparation of polymer blends with huge polarity difference.展开更多
Ammonia(NH3)is mainly produced via the Haber-Bosch process.It was discovered that the performance of a wide variety of catalysts in NH3 synthesis could be considerably enhanced by the addition of rare earth elements(R...Ammonia(NH3)is mainly produced via the Haber-Bosch process.It was discovered that the performance of a wide variety of catalysts in NH3 synthesis could be considerably enhanced by the addition of rare earth elements(REEs).As a result,catalysts promoted by REEs,especially the Ru-based ones have been extensively investigated.In this review,we summarize the progress of utilizing REEs for ammonia synthesis and outline the prospects of using them in the design and development of highly efficient and stable catalysts for ammonia synthesis.展开更多
In this paper, environmental scanning electron microscopy （ESEM） is applied to characterizing the mineral and element distribution of chromite ore processing residue （COPR）. The test results show that Cr-bearing b...In this paper, environmental scanning electron microscopy （ESEM） is applied to characterizing the mineral and element distribution of chromite ore processing residue （COPR）. The test results show that Cr-bearing brownmillerite occurs in the rim of COPR particle, while hydroandradite with Cr （Ⅵ） in its structure presents inside the COPR particle. Periclase and calcite occur in the interstitial area. Element analyses show that Ca, Fe and Al are distributed throughout the COPR particle, and Mg exists mostly in the interstitial area or on the particle surface. A lower content of Cr is evenly distributed in the COPR particle, while slightly higher concentration of Cr occurs inside the particle. It is suggested that it will take a relatively longer time for Cr to migrate out of COPR, especially fbr hexavalent chromium, so the leaching time and the particle size may be two important factors to affect the release of Cr （Ⅵ）.展开更多
This study described a hydrometallurgical method to investigate the separation of rare earth elements（REEs）from rare earth polishing powder wastes（REPPWs）containing large amounts of rare earth oxides with a major ...This study described a hydrometallurgical method to investigate the separation of rare earth elements（REEs）from rare earth polishing powder wastes（REPPWs）containing large amounts of rare earth oxides with a major phase of CeO2 and minor phases of La2O3,Pr2O3,and Nd2O3 using a process devised by the authors.The suggested approach consisted of five processes：the synthesis of NaR E（SO4）2·xH2O from rare earth oxides in Na2SO4-H2SO4-H2 O solutions（Process 1）,the conversion of NaR E（SO4）2·xH2O into RE（OH）3 using NaO H（Process 2）,and the oxidation of Ce（OH）3 into Ce（OH）4 using air with O2 injection（Process 3）,followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H2SO4,respectively.To confirm the high yield of NaR E（SO4）2·xH2O in Process 1,experiments were carried out under various Na2SO4 concentrations（0.4–2.5 mol/L）,sulfuric acid concentrations（6–14 mol/L）,and reaction temperatures（95–125 oC）.In addition,the effect of the pH value on the separation of Ce（OH）4 in HCl-H2 O solutions with Ce（OH）4,La-,Pr-,and Nd（OH）3 in Process 4 was also investigated.On the basis of above results,the possibility of effective separation of REEs from REPPWs could be confirmed.展开更多
The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of tal...The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.展开更多
Nine horizon samples of three soil profiles representative of Dystri-gelic Cambisol, Fibri-gelic Histosoland Relic Ornithosol were taken from Fildes Peninsula of King George Island, Antarctica, to quantitativelydemons...Nine horizon samples of three soil profiles representative of Dystri-gelic Cambisol, Fibri-gelic Histosoland Relic Ornithosol were taken from Fildes Peninsula of King George Island, Antarctica, to quantitativelydemonstrate the enrichment, migration and loss of the elements (Si, Al, Fe, Ca, Mg, Mn, K, Na and P) insoil horizons and their behaviours within profiles by application of the concept of the enrichment coefficientcalculated in terms of the abundance of Ti. Besides, six horizon samples of 4 other profiles randomly takenfrom the studied area were examined for calculation of the redistributing enrichment coefficient, which wasapplied for a better understanding of the element redistribution between soil and clay fraction along with soildevelopment. The results showed that the enrichment, migration and redistribution of the elements variedstrongly among the investigated soils and horizons, due to the differences of weathering degrees and moisturestatus, influences of sea bird activities, etc.展开更多
Municipal sludge is produced in large amounts and is difficult to treat.Incineration is the most direct and thorough treatment method.In order to study the feasibility of sintering for municipal sludge treatment,the m...Municipal sludge is produced in large amounts and is difficult to treat.Incineration is the most direct and thorough treatment method.In order to study the feasibility of sintering for municipal sludge treatment,the municipal sludge reforming process was studied under high-temperature oxidation conditions.The results showed that the sludge reforming process could be divided into four stages:the precipitation and evaporation of adsorbed water,the precipitation and combustion of the volatile,the combustion of the residual volatile and solid carbon,and the decomposition of salts and the melting of sludge.An increase in the heating rate resulted in more intense sludge combustion and improved the sludge reaction capacity and combustion performance.After burning at 1300℃,Si,Ca,Mg,Al,K,Na,and Cu formed new phases and entered the slag.75%of P remained in the slag.80%of the S formed SO_(2) and entered the flue gas.Cl formed gaseous chlorides like HCl upon combustion and entered the flue gas.As sintering is a feasible method for treating municipal sludge,care must be taken to limit the amount of P that ends up in the ore.展开更多
The effect of tramp elements in the steel was intensively studied. It was found that the solubility of tramp elements decreased as the temperature decreased under normal cooling conditions. The tramp elements （Cu, Pb...The effect of tramp elements in the steel was intensively studied. It was found that the solubility of tramp elements decreased as the temperature decreased under normal cooling conditions. The tramp elements （Cu, Pb, and Sn） diffused toward the grain boundaries, and intermetallic compounds or rich phases which have low melting points were formed, causing reduction in ductility and failure during the bending test. Rebars with Cu content which were left to air cooling after the last step showed drop in elongation, up to 32 %. On contrast, the samples with high per- centage of tramp elements （Cu, Pb, and Sn） in the billet, which were rolled and subjected to Tempcore process, did not show drop in elongation or failure in bending test （especially for rebar with diameter less than 32 mm）; however, copper must be less than 0.35 mass% to prevent the precipitation of Cu-rich zones of critical size in 32 mm. When quench- ing was applied, the tramp elements remained in the interstitial supersaturated solid solution positions inside the grains and would not have the chance to diffuse and form precipitates, hindering the copper precipitates from reac- hing the critical size necessary for impairing the properties. This would hinder the occurrence of the harmful effect of the tramp elements on the elongation or the hot shortness after rolling.展开更多
Fluid-structure interaction （FSI） problems in microchannels play a prominent role in many engineering applications. The present study is an effort toward the simulation of flow in microchannel considering FSI. The b...Fluid-structure interaction （FSI） problems in microchannels play a prominent role in many engineering applications. The present study is an effort toward the simulation of flow in microchannel considering FSI. The bottom boundary of the microchannel is simulated by size-dependent beam elements for the finite element method （FEM） based on a modified cou- ple stress theory. The lattice Boltzmann method （LBM） using the D2Q13 LB model is coupled to the FEM in order to solve the fluid part of the FSI problem. Because of the fact that the LBM generally needs only nearest neighbor information, the algorithm is an ideal candidate for parallel computing. The simulations are carried out on graphics processing units （GPUs） using computed unified device architecture （CUDA）. In the present study, the governing equations are non-dimensionalized and the set of dimensionless groups is exhibited to show their effects on micro-beam displacement. The numerical results show that the displacements of the micro-beam predicted by the size-dependent beam element are smaller than those by the classical beam element.展开更多
Mg-3.99Y-3.81Nd-0.53 Zr(WE43)casting alloy was subjected to single-pass friction stir processing(FSP)at a constant processing speed of 60 mm-min^(-1)and various rotation speeds of 400,800,1200,and 1500 r·min^(-1)...Mg-3.99Y-3.81Nd-0.53 Zr(WE43)casting alloy was subjected to single-pass friction stir processing(FSP)at a constant processing speed of 60 mm-min^(-1)and various rotation speeds of 400,800,1200,and 1500 r·min^(-1),and microstructures and mechanical properties of the experimental materials were investigated.FSP results in the generation of fine-grained microstructure,and fundamental breakage and dissolution of the coarse second phases.With the rotation speeds increasing,the average grain size of the FSP specimen in the stir zone first decreases and then increases,and the finest microstructure(~2μm)was prepared at the rotation speed of 800 r·min^(-1).Owing to the finer and more uniform microstructure,the mechanical properties of WE43 alloy after FSP are significantly improved.The variation tendency of the tensile properties is consistent with the change of the grain size.The maximum tensile strength,elongation,and average microhardness of the FSP WE43 alloy obtained at 800 r·min^(-1)are 290 MPa,17.2%,and HV92.9,respectively.The fracture morphology shows that small dimples can be observed on the FSP specimens,while the as-cast alloy fails through cleavage fracture.展开更多
In the analysis of high-rise building, traditional displacement-based plane elements are often used to get the in-plane internal forces of the shear walls by stress integration. Limited by the singular problem produce...In the analysis of high-rise building, traditional displacement-based plane elements are often used to get the in-plane internal forces of the shear walls by stress integration. Limited by the singular problem produced by wall holes and the loss of precision induced by using differential method to derive strains, the displacement-based elements cannot always present accuracy enough for design. In this paper, the hybrid post-processing procedure based on the Hellinger-Reissner variational principle is used for improving the stress precision of two quadrilateral plane elements. In order to find the best stress field, three different forms are assumed for the displacement-based plane elements and with drilling DOF. Numerical results show that by using the proposed method, the accuracy of stress solutions of these two displacement-based plane elements can be improved.展开更多
Design a precision electroplating mechanical structure for automobiles based on finite element analysis method and analyze its mechanical properties.Taking the automobile steering knuckle as the research object,ABAQUS...Design a precision electroplating mechanical structure for automobiles based on finite element analysis method and analyze its mechanical properties.Taking the automobile steering knuckle as the research object,ABAQUS parametric modeling technology is used to construct its three-dimensional geometric model,and geometric simplification is carried out.Two surface treatment processes,HK-35 zinc nickel alloy electroplating and pure zinc electroplating,were designed,and the influence of different coatings on the mechanical properties of steering knuckles was compared and analyzed through numerical simulation.At the same time,standard specimens were prepared for salt spray corrosion testing and scratch method combined strength testing to verify the numerical simulation results.The results showed that under emergency braking and composite working conditions,the peak Von Mises stress of the zinc nickel alloy coating was 119.85 MPa,which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Its equivalent strain value was 652×10^(-6),which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Experimental data confirms that zinc nickel alloy coatings exhibit significant advantages in stress distribution uniformity,strain performance,and load-bearing capacity in high stress zones.The salt spray corrosion test further indicates that the coating has superior corrosion resistance and coating substrate interface bonding strength,which can significantly improve the mechanical stability and long-term reliability of automotive precision electroplating mechanical structures.展开更多
Indigenous cultures prescribed a means of maximizing the benefits they produced and enjoyed in their relationship with each other and the environment-based on their understanding of the nature of existence and how to ...Indigenous cultures prescribed a means of maximizing the benefits they produced and enjoyed in their relationship with each other and the environment-based on their understanding of the nature of existence and how to live in harmony with the forces shaping the nature of existence.The emergence of civilization introduced the claim that rational abilities superseded indigenous knowledge.This was followed by positivism and the claim that knowledge passed through three stages:mythological,philosophical,and scientific.This impacted indigenous cultures in ways that reached a height when postcolonial development experts convinced national leaders that progress required adopting advances in science.A failure to modernize was regarded as holding back progress.With the development paradigm now regarded as inadequate for achieving its goals and with the rise of the sustainability discourse,there is appreciation for indigenous knowledge.This article describes an indigenous cultural knowledge system that reflects the insight and wisdom of the world’s most respected scientific and philosophical traditions.The beliefs of the Bodo people of Northeast India are used as an example of an indigenous worldview that portrays insight proven to have value that is comparable to the natural sciences,plus theories of natural law and political philosophy.展开更多
Percussive drilling is gaining interest for both shallow and deep applications due to its potential for higher drilling rates in hard rocks.Therefore,for efficient rock breaking,the development of advanced percussive ...Percussive drilling is gaining interest for both shallow and deep applications due to its potential for higher drilling rates in hard rocks.Therefore,for efficient rock breaking,the development of advanced percussive drilling simulation tools has the potential to be transformative.Such tools must accurately capture the rock’s response to enable an effective analysis of the fragmentation process.Traditional continuum numerical methods,such as the finite element method(FEM),do not simulate discrete cracks or the contact interaction between rock fragments.The finite-discrete element method(FDEM)is a three-dimensional hybrid method that combines FEM with the discrete element method(DEM)that addresses these limitations.New FDEM simulation results of impacts on Kuru Grey granite show good agreement with published experimental data.The interpretation focuses on two significant processes in percussive drilling:crack propagation and chipping generation.FDEM successfully simulates the evolution of cracks,including radial,side,and inclined cracks,as well as crushed and cracked zones.The simulation also reproduces the coalescence of adjacent craters to generate more chippings.Additionally,the stress state,velocity field and discrete fractures simulated by FDEM provide detailed insights into the different fracture patterns for Kuru Grey granite,enhancing understanding of the fundamental underlying mechanisms.展开更多
Sandy braided river deposits are widely preserved in ancient stratigraphic records and act as a significant type of hydrocarbon reservoir.Due to the frequent and rapid migration of channels within the riverbed,the sed...Sandy braided river deposits are widely preserved in ancient stratigraphic records and act as a significant type of hydrocarbon reservoir.Due to the frequent and rapid migration of channels within the riverbed,the sedimentary architecture is highly complex.In this paper,a flume experiment was conducted to reveal the detailed depositional process and establish a fine sedimentary architecture model for sandy braided rivers.The result showed that(1)Three types of braid channels,including the lateral migration channel,the confluence channel,and the deep incised channel,were recognized based on geometry,scale,distribution,and spatial patterns;they are interconnected,forming a complex channel network.(2)Braid channels were characterized by lateral migration,abandonment,filling,and chute cutoff.Lateral migration of channels shaped the braid bars and dominated the formation,growth,and reworking of braid bars.(3)Controlled by the fast and frequent variations of the braid channel network,braid bars were continuously formed,reworked,reshaped,and composited of multiple accretions with different types,orientations,scales,and preservation degrees.Symmetrical and asymmetrical braid bars pre-sented significantly different composition patterns.(4)Dominated by the continuous reworking of braid channels,temporary deposits were limited preserved,braid channel deposits account for 54.3 percent of the eventually preserved braided river deposits,and four types of amalgamate patterns were recognized.Braid bars were cut and limited preserved,only accounting for 45.7 percent of the eventually preserved braided river deposits.(5)During the experiment,only 28 percent of near-surface temporary deposits were eventually preserved in fragmented forms with the final experimental braided river;the shape,spatial patterns,and most of the deposits observed during the depositional process were largely reworked and poorly preserved.(6)The scale of eventually preserved braid bars and braid channels is significantly smaller than the temporary deposits from geomorphic observations.The aspect ratio of the eventually preserved braid bars and the width-to-depth ratio of the eventually preserved braid channel are also significantly different from that of the temporary ones measured from topography data.展开更多
基金Project(2009ZX04005-031-11)supported by the Major National Science and Technology Special Project of ChinaProject(318968)supported by the Marie Curie International Research Staff Exchange Scheme(IRSES,Mat Pro Future)within the 7th EC Framework Program(FP7)Project(B08040)supported by the 111 Plan,China
文摘Identifying suitable processing window is necessary but difficult for achieving favorable microstructure and performance in extrusion of large thick-walled pipe with difficult-to-deform Inconel 625 alloy. In this work, a method was established for identifying the extrusion process window considering temperature control using response surface methodology. Firstly, the response surface models, which correlate temperature rise and peak temperature to key extrusion parameters, have been developed by orthogonal regression based on finite element calculated data. Secondly, the coupled effects of the key extrusion parameters on the temperature rise and peak temperature have been disclosed based on the regression models. Lastly, suitable extrusion processing windows, which are described by contour map of peak temperature in the space of extrusion speed and initial billet temperature, have been established for different extrusion ratios. Using the identified process window, a suitable combination of the key extrusion parameters can be determined conveniently and quickly.
基金financially supported by the National Natural Science Foundation of China(No.51301017)the Fundamental Research Funds for the Central Universities of China(No.FRF-TP-13-034A)
文摘The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testing was performed in various Zn and Mg contents under different annealing and cold-rolling conditions. In the results, the stress drop and reloading time of serrations increase with increasing plastic strain and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg or Zn content. The alloys with a greater intensity of serrated yielding generally exhibit a greater elongation. The stress drop and reloading time of serrations decrease with increasing grain size in the case of the annealed samples. The cold-rolled sample exhibits the most severe serra- tion because it initially contains a large number of grain boundaries and dislocations.
文摘Austempered ductile iron(ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called "ausferrite" that is the result of austempering heat treatment applied to ductile irons. Alloying elements increase ADI austemperability and change speeds of austempering reactions. Thus, they can affect ADI resultant microstructure and mechanical properties. In this paper, the effects of alloying elements on ADI mechanical properties, microstructural changes, two-stage austempering reactions, processing windows, austemperability, and other aspects are reviewed.
基金This research was supported by the Department of Mining Engineering at the University of Utah.In addition,the lead author wishes to acknowledge the financial support received from the Talent Introduction Project,part of the Elite Program of Shandong University of Science and Technology(No.0104060540171).
文摘This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing(DIP) and discrete element method(DEM). The results showed that the X-ray diffraction(XRD)-based DIP method effectively analyzed the mineral composition contents and spatial distributions of granite. During the particle flow code(PFC2D) model calibration phase, the numerical simulation exhibited that the uniaxial compressive strength(UCS) value, elastic modulus(E), and failure pattern of the granite specimen in the UCS test were comparable to the experiment. By establishing 351 sets of numerical models and exploring the impacts of mineral composition on the mechanical properties of granite, it indicated that there was no negative correlation between quartz and feldspar for UCS, tensile strength(σ_(t)), and E. In contrast, mica had a significant negative correlation for UCS, σ_(t), and E. The presence of quartz increased the brittleness of granite, whereas the presence of mica and feldspar increased its ductility in UCS and direct tensile strength(DTS) tests. Varying contents of major mineral compositions in granite showed minor influence on the number of cracks in both UCS and DTS tests.
基金This work was financially supported by the National Natural Science Foundation of China(No.51421061).
文摘In this work, completely immiscible polyethylene/polyamidel2 （PE/PA12） blends were prepared by high shear extruder. The morphology and mechanical properties of the blends were investigated as a function of rotation speed. It was found that the high shear processing is an effective method to improve the dispersion of the PAl2 phase in PE matrix when PA 12 contents are 5 wt% and 10 wt%, and the dispersed phase particle size is reduced with the increase of rotation speed from 100 r/min to 500 r/min. However, with further increase of PAl2 content to 20 wt%, high shear processing has no effect on the phase morphology of the blends. Accordingly, a largely increased elongation at break and impact strength are observed for PE/PAl2/95/5 and PE/PA12/90/10 blends obtained at high rotation speeds but no effect on the property of PE/PAI2/80/20. Annealing experiment demonstrated that the obtained phase morphology is not stable thus compatibilizer should be introduced in the future work. This work could provide a guideline for the application of high shear processing in the preparation of polymer blends with huge polarity difference.
基金Project supported by the National Natural Science Foundation of China(22038002,21972019)。
文摘Ammonia(NH3)is mainly produced via the Haber-Bosch process.It was discovered that the performance of a wide variety of catalysts in NH3 synthesis could be considerably enhanced by the addition of rare earth elements(REEs).As a result,catalysts promoted by REEs,especially the Ru-based ones have been extensively investigated.In this review,we summarize the progress of utilizing REEs for ammonia synthesis and outline the prospects of using them in the design and development of highly efficient and stable catalysts for ammonia synthesis.
基金Supported by National Natural Science Foundation of China (No. 50808091)
文摘In this paper, environmental scanning electron microscopy （ESEM） is applied to characterizing the mineral and element distribution of chromite ore processing residue （COPR）. The test results show that Cr-bearing brownmillerite occurs in the rim of COPR particle, while hydroandradite with Cr （Ⅵ） in its structure presents inside the COPR particle. Periclase and calcite occur in the interstitial area. Element analyses show that Ca, Fe and Al are distributed throughout the COPR particle, and Mg exists mostly in the interstitial area or on the particle surface. A lower content of Cr is evenly distributed in the COPR particle, while slightly higher concentration of Cr occurs inside the particle. It is suggested that it will take a relatively longer time for Cr to migrate out of COPR, especially fbr hexavalent chromium, so the leaching time and the particle size may be two important factors to affect the release of Cr （Ⅵ）.
文摘This study described a hydrometallurgical method to investigate the separation of rare earth elements（REEs）from rare earth polishing powder wastes（REPPWs）containing large amounts of rare earth oxides with a major phase of CeO2 and minor phases of La2O3,Pr2O3,and Nd2O3 using a process devised by the authors.The suggested approach consisted of five processes：the synthesis of NaR E（SO4）2·xH2O from rare earth oxides in Na2SO4-H2SO4-H2 O solutions（Process 1）,the conversion of NaR E（SO4）2·xH2O into RE（OH）3 using NaO H（Process 2）,and the oxidation of Ce（OH）3 into Ce（OH）4 using air with O2 injection（Process 3）,followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H2SO4,respectively.To confirm the high yield of NaR E（SO4）2·xH2O in Process 1,experiments were carried out under various Na2SO4 concentrations（0.4–2.5 mol/L）,sulfuric acid concentrations（6–14 mol/L）,and reaction temperatures（95–125 oC）.In addition,the effect of the pH value on the separation of Ce（OH）4 in HCl-H2 O solutions with Ce（OH）4,La-,Pr-,and Nd（OH）3 in Process 4 was also investigated.On the basis of above results,the possibility of effective separation of REEs from REPPWs could be confirmed.
基金Project(2013BAB06B00) supported by the National Key Technology R&D Programof ChinaProject(2011CB013504) supported by the National Basic Research Program of ChinaProject(50911130366) supported by the National Natural Science Foundation of China
文摘The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.
文摘Nine horizon samples of three soil profiles representative of Dystri-gelic Cambisol, Fibri-gelic Histosoland Relic Ornithosol were taken from Fildes Peninsula of King George Island, Antarctica, to quantitativelydemonstrate the enrichment, migration and loss of the elements (Si, Al, Fe, Ca, Mg, Mn, K, Na and P) insoil horizons and their behaviours within profiles by application of the concept of the enrichment coefficientcalculated in terms of the abundance of Ti. Besides, six horizon samples of 4 other profiles randomly takenfrom the studied area were examined for calculation of the redistributing enrichment coefficient, which wasapplied for a better understanding of the element redistribution between soil and clay fraction along with soildevelopment. The results showed that the enrichment, migration and redistribution of the elements variedstrongly among the investigated soils and horizons, due to the differences of weathering degrees and moisturestatus, influences of sea bird activities, etc.
基金This work was supported by Ministry of Science and Technology of the People’s Republic of China(2019YFC1904600).
文摘Municipal sludge is produced in large amounts and is difficult to treat.Incineration is the most direct and thorough treatment method.In order to study the feasibility of sintering for municipal sludge treatment,the municipal sludge reforming process was studied under high-temperature oxidation conditions.The results showed that the sludge reforming process could be divided into four stages:the precipitation and evaporation of adsorbed water,the precipitation and combustion of the volatile,the combustion of the residual volatile and solid carbon,and the decomposition of salts and the melting of sludge.An increase in the heating rate resulted in more intense sludge combustion and improved the sludge reaction capacity and combustion performance.After burning at 1300℃,Si,Ca,Mg,Al,K,Na,and Cu formed new phases and entered the slag.75%of P remained in the slag.80%of the S formed SO_(2) and entered the flue gas.Cl formed gaseous chlorides like HCl upon combustion and entered the flue gas.As sintering is a feasible method for treating municipal sludge,care must be taken to limit the amount of P that ends up in the ore.
文摘The effect of tramp elements in the steel was intensively studied. It was found that the solubility of tramp elements decreased as the temperature decreased under normal cooling conditions. The tramp elements （Cu, Pb, and Sn） diffused toward the grain boundaries, and intermetallic compounds or rich phases which have low melting points were formed, causing reduction in ductility and failure during the bending test. Rebars with Cu content which were left to air cooling after the last step showed drop in elongation, up to 32 %. On contrast, the samples with high per- centage of tramp elements （Cu, Pb, and Sn） in the billet, which were rolled and subjected to Tempcore process, did not show drop in elongation or failure in bending test （especially for rebar with diameter less than 32 mm）; however, copper must be less than 0.35 mass% to prevent the precipitation of Cu-rich zones of critical size in 32 mm. When quench- ing was applied, the tramp elements remained in the interstitial supersaturated solid solution positions inside the grains and would not have the chance to diffuse and form precipitates, hindering the copper precipitates from reac- hing the critical size necessary for impairing the properties. This would hinder the occurrence of the harmful effect of the tramp elements on the elongation or the hot shortness after rolling.
文摘Fluid-structure interaction （FSI） problems in microchannels play a prominent role in many engineering applications. The present study is an effort toward the simulation of flow in microchannel considering FSI. The bottom boundary of the microchannel is simulated by size-dependent beam elements for the finite element method （FEM） based on a modified cou- ple stress theory. The lattice Boltzmann method （LBM） using the D2Q13 LB model is coupled to the FEM in order to solve the fluid part of the FSI problem. Because of the fact that the LBM generally needs only nearest neighbor information, the algorithm is an ideal candidate for parallel computing. The simulations are carried out on graphics processing units （GPUs） using computed unified device architecture （CUDA）. In the present study, the governing equations are non-dimensionalized and the set of dimensionless groups is exhibited to show their effects on micro-beam displacement. The numerical results show that the displacements of the micro-beam predicted by the size-dependent beam element are smaller than those by the classical beam element.
基金the Fundamental Research Funds for the Central Universities(No.2012ZZ0051)。
文摘Mg-3.99Y-3.81Nd-0.53 Zr(WE43)casting alloy was subjected to single-pass friction stir processing(FSP)at a constant processing speed of 60 mm-min^(-1)and various rotation speeds of 400,800,1200,and 1500 r·min^(-1),and microstructures and mechanical properties of the experimental materials were investigated.FSP results in the generation of fine-grained microstructure,and fundamental breakage and dissolution of the coarse second phases.With the rotation speeds increasing,the average grain size of the FSP specimen in the stir zone first decreases and then increases,and the finest microstructure(~2μm)was prepared at the rotation speed of 800 r·min^(-1).Owing to the finer and more uniform microstructure,the mechanical properties of WE43 alloy after FSP are significantly improved.The variation tendency of the tensile properties is consistent with the change of the grain size.The maximum tensile strength,elongation,and average microhardness of the FSP WE43 alloy obtained at 800 r·min^(-1)are 290 MPa,17.2%,and HV92.9,respectively.The fracture morphology shows that small dimples can be observed on the FSP specimens,while the as-cast alloy fails through cleavage fracture.
文摘In the analysis of high-rise building, traditional displacement-based plane elements are often used to get the in-plane internal forces of the shear walls by stress integration. Limited by the singular problem produced by wall holes and the loss of precision induced by using differential method to derive strains, the displacement-based elements cannot always present accuracy enough for design. In this paper, the hybrid post-processing procedure based on the Hellinger-Reissner variational principle is used for improving the stress precision of two quadrilateral plane elements. In order to find the best stress field, three different forms are assumed for the displacement-based plane elements and with drilling DOF. Numerical results show that by using the proposed method, the accuracy of stress solutions of these two displacement-based plane elements can be improved.
文摘Design a precision electroplating mechanical structure for automobiles based on finite element analysis method and analyze its mechanical properties.Taking the automobile steering knuckle as the research object,ABAQUS parametric modeling technology is used to construct its three-dimensional geometric model,and geometric simplification is carried out.Two surface treatment processes,HK-35 zinc nickel alloy electroplating and pure zinc electroplating,were designed,and the influence of different coatings on the mechanical properties of steering knuckles was compared and analyzed through numerical simulation.At the same time,standard specimens were prepared for salt spray corrosion testing and scratch method combined strength testing to verify the numerical simulation results.The results showed that under emergency braking and composite working conditions,the peak Von Mises stress of the zinc nickel alloy coating was 119.85 MPa,which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Its equivalent strain value was 652×10^(-6),which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Experimental data confirms that zinc nickel alloy coatings exhibit significant advantages in stress distribution uniformity,strain performance,and load-bearing capacity in high stress zones.The salt spray corrosion test further indicates that the coating has superior corrosion resistance and coating substrate interface bonding strength,which can significantly improve the mechanical stability and long-term reliability of automotive precision electroplating mechanical structures.
文摘Indigenous cultures prescribed a means of maximizing the benefits they produced and enjoyed in their relationship with each other and the environment-based on their understanding of the nature of existence and how to live in harmony with the forces shaping the nature of existence.The emergence of civilization introduced the claim that rational abilities superseded indigenous knowledge.This was followed by positivism and the claim that knowledge passed through three stages:mythological,philosophical,and scientific.This impacted indigenous cultures in ways that reached a height when postcolonial development experts convinced national leaders that progress required adopting advances in science.A failure to modernize was regarded as holding back progress.With the development paradigm now regarded as inadequate for achieving its goals and with the rise of the sustainability discourse,there is appreciation for indigenous knowledge.This article describes an indigenous cultural knowledge system that reflects the insight and wisdom of the world’s most respected scientific and philosophical traditions.The beliefs of the Bodo people of Northeast India are used as an example of an indigenous worldview that portrays insight proven to have value that is comparable to the natural sciences,plus theories of natural law and political philosophy.
文摘Percussive drilling is gaining interest for both shallow and deep applications due to its potential for higher drilling rates in hard rocks.Therefore,for efficient rock breaking,the development of advanced percussive drilling simulation tools has the potential to be transformative.Such tools must accurately capture the rock’s response to enable an effective analysis of the fragmentation process.Traditional continuum numerical methods,such as the finite element method(FEM),do not simulate discrete cracks or the contact interaction between rock fragments.The finite-discrete element method(FDEM)is a three-dimensional hybrid method that combines FEM with the discrete element method(DEM)that addresses these limitations.New FDEM simulation results of impacts on Kuru Grey granite show good agreement with published experimental data.The interpretation focuses on two significant processes in percussive drilling:crack propagation and chipping generation.FDEM successfully simulates the evolution of cracks,including radial,side,and inclined cracks,as well as crushed and cracked zones.The simulation also reproduces the coalescence of adjacent craters to generate more chippings.Additionally,the stress state,velocity field and discrete fractures simulated by FDEM provide detailed insights into the different fracture patterns for Kuru Grey granite,enhancing understanding of the fundamental underlying mechanisms.
基金funded by two projects of the National Natural Science Foundation of China(No.41802123,42130813).
文摘Sandy braided river deposits are widely preserved in ancient stratigraphic records and act as a significant type of hydrocarbon reservoir.Due to the frequent and rapid migration of channels within the riverbed,the sedimentary architecture is highly complex.In this paper,a flume experiment was conducted to reveal the detailed depositional process and establish a fine sedimentary architecture model for sandy braided rivers.The result showed that(1)Three types of braid channels,including the lateral migration channel,the confluence channel,and the deep incised channel,were recognized based on geometry,scale,distribution,and spatial patterns;they are interconnected,forming a complex channel network.(2)Braid channels were characterized by lateral migration,abandonment,filling,and chute cutoff.Lateral migration of channels shaped the braid bars and dominated the formation,growth,and reworking of braid bars.(3)Controlled by the fast and frequent variations of the braid channel network,braid bars were continuously formed,reworked,reshaped,and composited of multiple accretions with different types,orientations,scales,and preservation degrees.Symmetrical and asymmetrical braid bars pre-sented significantly different composition patterns.(4)Dominated by the continuous reworking of braid channels,temporary deposits were limited preserved,braid channel deposits account for 54.3 percent of the eventually preserved braided river deposits,and four types of amalgamate patterns were recognized.Braid bars were cut and limited preserved,only accounting for 45.7 percent of the eventually preserved braided river deposits.(5)During the experiment,only 28 percent of near-surface temporary deposits were eventually preserved in fragmented forms with the final experimental braided river;the shape,spatial patterns,and most of the deposits observed during the depositional process were largely reworked and poorly preserved.(6)The scale of eventually preserved braid bars and braid channels is significantly smaller than the temporary deposits from geomorphic observations.The aspect ratio of the eventually preserved braid bars and the width-to-depth ratio of the eventually preserved braid channel are also significantly different from that of the temporary ones measured from topography data.
